The hardware, or physical components, of a computer consists of a PROCESSOR, MEMORY, INPUT AND OUTPUT (I/0) devices, and STORAGE. The processing function is divided between the processor and memory. The processor is the brain of the machine. Memory holds data and program instructions as the CPU works with them. The most common units of measure for memory are the bits and bytes

Bit 8 = 1 KB (Kilo Byte)

1024 KB = 1 MB (Mega Byte)

1024 MB = 1 GB (Giga Byte)

1024 GB = 1 TB (Tera Byte)

1024 TB = 1 PB (Peta Byte)

1024 PB = 1 EB (Exa Byte)

1024 EB = 1 ZB (Zetta Byte)

1024 ZB = 1 YB (Yotta Byte)

INPUT DEVICES

The Keyboard

# A standard computer keyboard has about 100 keys; each key sends a different signal to the CPU. Most keyboards follow a similar layout, with their keys arranged in five groups. Those groups include the alphanumeric keys, numeric keypad, function keys, mod­ifier keys, and cursor-movement keys. Most keyboards use the QWERTY layout, which gets its name from the first six keys in the top row of letters. When you press a key, the keyboard controller notes that a key was pressed and places a code in the keyboard buffer to indicate which key was pressed. The keyboard sends the computer an interrupt request, which tells the CPU to accept the keystroke. (Keyboard Type; AT, ATX or PS/2, USB, Wireless)

The Mouse

# The mouse is a pointing device that lets you control the position of a graphical pointer on the screen without using the keyboard. Using the mouse involves five techniques: pointing, click­ing, double-clicking, dragging, and right-clicking. (Mouse Type; Seriel, ATX or PS/2, USB, Wireless)

Variants Of The Mouse

# A trackball is like a mouse turned upside-down. It provides the func­tionality of a mouse-but takes less space on the desktop. A track pad is a touch-sensitive pad that may be built into the keyboard or added to the PC as a separate unit. It provides the same function­ality as a mouse. To use a track­ pad, you glide your finger across its surface

# With a pen-based system, you use a "pen" (also called a stylus) to write on a special pad or directly on the screen.

# Touch-screen systems accept input directly through the monitor. Touch-screen systems are useful for selecting options from menus, but they are not useful for inputting text or other types of data in large quantities.

# A Game Controller is a special input device that accepts the user's input for playing a game. The two primary types of game controllers are joysticks and game pads.

# Bar code readers, such as those used in grocery stores, can read bar codes, translate them into numbers, and input the numbers into a computer system.

# Image scanners convert printed images into digitized formats that can be stored and manipulated in computers. An image scanner equipped with OCR software can translate a page of text into a string of character codes in the computer's memory.

# Microphones can accept auditory input. Using speech-recognition software, you can use your microphone as an input device for dictating text, navigating programs, and choosing commands.

# Pc Video Cameras and digital cameras can digitize full-motion and still images, which can be stored and edited on the PC or transmit­ted over a LAN or the Internet.

DEVICES THAT OUTPUT SOFT COPY

Monitors

@ Computer monitors are roughly divided into two categories: CRT and flat-panel (LCD) displays. Monitors can also be categorized by the number of colors they display. Monitors are usually monochrome, grayscale, or color. A CRT monitor works with one or more ELECTRON GUNS that system­atically aim a beam of electrons at every pixel on the screen. Most LCD displays are either active matrix or passive matrix.

@ When purchasing a monitor, you should consider its size, resolution, refresh rate, and dot pitch.

@ The video controller is an interface between the monitor and the CPU. The video controller determines many aspects of a monitor's performance; for example, the video controller lets you select a resolution or set the number of colors to display.

Personal Computer Projectors

@ A PC projector is a portable light projector that connects to a PC. This type of projector is rapidly replacing traditional slide projectors and Overhead projectors as a means for displaying presentations.

Sound systems

@ Multimedia PCs generally come with sound systems, which include a sound card, SPEAKERS, a CD-ROM or DVD drive, and a video controller.

DEVICES THAT OUTPUT HARD COPY

Printers

Printers fall into two general categories:

1. Impact

2. Non impact.

@Impact printers create an image on paper by using a device to strike an inked ribbon, pressing ink from the ribbon onto the paper. Non impact printers use various methods to place ink on the page. When evaluating printers for purchase, you should consider four criteria: image quality, speed, initial cost, and cost of operation.

Dot Matrix Printers

A dot matrix printer is a common type of impact printer. A dot matrix printer uses a print head, which contains a cluster of pins. The printer can push the pins out to form patterns, in rapid sequence. The pins are used to press an inked ribbon against paper, thus cre­ating an image. The lowest resolution dot matrix printers have an array of nine pins(9); the highest resolution dot matrix printers have twenty-four (24) pins.The speed of dot matrix printers is measured in charac­ters per second (cps).

Ink Jet Printers

An ink jet printer is an example of a non impact printer. It creates an image by spraying tiny droplets of ink onto the paper. Ink jet printers are inexpensive for both color and black printing, have low operating costs, and offer quality and speed comparable to low-end laser printers.

Laser Printers

Laser printers produce higher quality print and are fast and convenient to use, but they are also more expensive than ink jet printers. Laser printers are non impact printers. They use heat and pressure to bond tiny particles of toner (a dry ink) to paper.

Snapshot Printers

Snapshot printers are specialized, small-format printers used to print small color photographs. Snapshot printers are popular among users who own digital cameras.